Perpendicular magnetic recording medium

Abstract

A perpendicular magnetic recording medium having an excellent thermal stability of the recorded signal and S/N and a low medium noise, and capable of easily forming a perpendicular magnetic recording layer is provided. The perpendicular magnetic recording medium has, at least, a perpendicular magnetic recording layer having a hexagonal closest packing (hcp) structure of which c-axis is perpendicular to a surface of the perpendicular magnetic recording layer, on a non-magnetic base, wherein the perpendicular magnetic recording layer has a saturation magnetization Ms of not more than 400 emu/cc, and a lattice constant c of the hexagonal closest packing structure is not more than 4.07 Å.

What is claimed is:  
     
       1. A perpendicular magnetic recording medium comprising, at least, a perpendicular magnetic recording layer having a hexagonal closest packing (hcp) structure of which c-axis is perpendicular to a surface of the perpendicular magnetic recording layer, on a non-magnetic base, wherein the perpendicular magnetic recording layer has a saturation magnetization Ms of not more than 400 emu/cc, and a lattice constant c of the hexagonal closest packing structure is not more than 4.07 Å, such that the coercivity Hc of the recording medium is not less than 2500 Oe and the squareness ratio Rs is not less than 0.6; and 
       wherein the magnetic recording layer comprises: a 4-element system alloy of Co—Cr—Nb—Ta, and when composition ratios of Nb and Ta are made to be x (at %) and y (at %), respectively, the 4-element system alloy satisfies inequalities (1) and (2) as follows:  
       
         
             x+y≧ 2  (1)  
         
       
       
         
           3 x/ 4+ y≦ 3  (2)  
         
       
       and 
       wherein x and y are each above zero.  
     
     
       2. A perpendicular magnetic recording medium comprising, at least, a perpendicular magnetic recording layer having a hexagonal closest packing (hcp) structure of which c-axis is perpendicular to a surface of the perpendicular magnetic recording layer, on a non-magnetic base, wherein the perpendicular magnetic recording layer has a saturation magnetization Ms of not more than 400 emu/cc, and a lattice constant c of the hexagonal closest packing structure is not more than 4.07 Å, such that the coercivity Hc of the recording medium is not less than 2500 Oe and the squareness ratio Rs is not less than 0.6; and 
       wherein a Co—Zr system amorphous soft magnetic under layer is formed under the perpendicular magnetic recording layer so that atoms of the perpendicular magnetic recording layer are directly coupled with atoms of the Co—Zr system amorphous soft magnetic under-layer.  
     
     
       3. A perpendicular magnetic recording medium as claimed in  claim 2 , wherein a pinning layer is formed under the Co—Zr system amorphous soft magnetic underlayer so as to pin magnetic domains of the Co—Zr system amorphous soft magnetic under-layer.